Tetrazo-dyes

The different behaviour of various textile fibres in dyeing may be explained by an assumption of different solvent power thus, silk dyes more readily than other fibres because the fibroin has a greater solvent power. Keratine again, the principle of the wool fibre, possesses a greater solvent power than cellulose, which is only capable of attracting and holding in solution a few dyestuffs, such as the tetrazo-dyes of the benzidine series, and in certain cases in this class the solvent power of the water in the dye-bath has to be decreased by addition of salt. 

This body [61] is known as CroceTn Scarlet 3B, and although not producing fast shades is used, in cotton-dyeing. Crocein Scarlet 7 B is a dyestuff of somewhat bluer shade, and is obtained from orthoamidoazotoluenesulphonic acid in the same manner. The tetrazo-dyes prepared from y3-naphthol- -sulphonic acid give soluble crystalline calcium salts, while those from the other acid give amorphous and insoluble calcium salts. 

Certain bacterial enzymatic actions, such as glucoslde cleavge, nltro reduction, and azo reduction for certain tetrazo dyes, are Involved In the activation of compounds In the Intestine. 

Congo Red is a tetrazo dye derived from benzidine. It is prepared by condensing the diazo compound from this amine with naphthionic acid, CioH6NH2.S03H(l, 4), and has the following formula —... 

Fastusol Yellow 66 [91-34-9] (25) (Cl Direct YeUow 4 Cl 24890) is a symmetrical primary disazo dye from a tetrazo component (4,4 diamino-2,2 stilbene-disulfonic acid [81-11-8],... 

Amidine Fast Red F [2429-84-7] (26) (Cl Direct Red 1 Cl 22310) is an iinsymmetrical primary disazo dye from a tetrazo component (benzidine... 

Congo Red.1—Dissolve 4-6 g. of benzidine in a hot mixture of 12 c.c. of concentrated hydrochloric acid and 100 c.c. of water, add 150 c.c. more water, cool the clear solution to 2°-3°, and diazotise with 3-6 g. of sodium nitrite in 20 c.c. of water, added within the space of one minute. Leave the tetrazo -solution for five minutes and then pour it with stirring into a solution of 16 g. of sodium naph-thionate and 20 g. of crystallised sodium acetate in 250 c.c. of water. When a sample of the liquid, on warming with hydrochloric acid, no longer evolves nitrogen, dissolve the blue-black precipitate of the dye-acid by warming with sodium carbonate and so produce the red sodium salt filter and salt out the product from the filtrate with common salt (not too much). Collect the precipitate at the pump and wash with brine. The blue acid can be precipitated from the solution of the sodium salt with hydrochloric acid. 

In addition, there are several tests that quantify cell number through a color development in the medium, including assays based on protein content, DNA content, lysosome and Golgi complex activity, enzymatic activity, and MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazo-lium bromide) dye reduction. 

In addition to Congo red, benzopurpurin 4 B, prepared from o-tolidine and naphthionic acid, is also of importance. In the preparation of this dye, the coupling reaction cannot be carried out at higher temperatures since the tetrazo compound from o-tolidine is too unstable. Benzopurpurin 4 B is somewhat less sensitive to acids than Congo red, and, like the latter, is widely used, particularly in the Orient. It is interesting that these dyes are found to be much more stable in nonindustrialized countries where the atmosphere contains little sulfuric and sulfurous acids. 

Coupling tetrazo (7) with o-cresol has been reported to give a dye (19) which is less alkali-sensitive than Direct Yellow 4 (Cl 24890) and to have better cold-water solubflity than Direct Yellow 12 (Cl 24895) (18). One reference is made to a stilbene laser dye (10) and two each to dyes for bght-polatizing films (34,35) and teprogtaphic inks (36,37). 

The diazotization of benzidine yielding diazo and tetrazo compounds, the coupling of these with phenols and amines yielding azo compounds, which are the benzidine dyes, should be recalled here (p. 569). 

On cotton they are generally incapable of complete fixation, as most of them form no real colour-lakes. Exceptions to this rule are certain tetrazo-compounds which dye cotton directly in the form of alkali salts of their sulphonic acids. 

The tetrazo-compounds obtained from benzidine and similar bases combine -with phenols and amines to produce yelloiTj red, bluCj and violet dyestuffs. These have attained considerable importance on account of their remarkable property of dyeing (in form of alkali salts) on unmordanted vegetable fibres. 

Azo-dyes prepared by interaction of a diazo-compound and a pbenol are insoluble in waterj and therefore of no practical value. For this reason a sulpho-group is introduced (see p. 34), and this produces the solubility necessary for their application in ordinary dyeing processes. These sulphonated azo-dyes have a considerable affinity for wool and silk, but (with the exception of those of the tetrazo-series) are not easily fixed on cotton. Cotton may be dyed with certain azo-dyes of the Crocein series, hut the shades produced are not fast to washing. 

Somenatural dyestuffs (Curcumin,Bixin,Carthamin) are capable, like the tetrazo dyestuffs, of dyeing on unmordanted cotton. 

The shades are very fast to soap. Like canarin and the direct dyeing tetrazo-colours, Cachou de Laval is capable of fixing basic dyestuffs, and the shades can thus be topped at will. 

Direct dyes. The first direct dye was Congo Red (Figure 2.26) obtained by tetrazotizing benzidine and coupling the tetrazo compound with 2 molecules of naphthionic acid (as sodium salt) in the presence of sodium acetate to act as buffer, i.e. 

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